White 2 (and or Black 2) is (are) definitely worth getting.. as the others have said the storyline is indeed a real sequel to Black & White and there are more features. While you cannot catch Tornadus or Thundurus directly in the game(s), you certainly have the chance to capture more Legendaries throughout the game. Also, the regional Pokédex in Black 2 and White 2 now consists of Pokémon from all generations, even at the beginning of the game, and not just Generation 5 Pokémon.

Zach has basically covered it all.

You should definitely get White 2, since you already have White and it's a continuation from White. Also, you get Reshiram in White 2 like how you get Zekrom in White.

And this is not just some improved game like Emerald or Platinum or Crystal or Yellow, this is a real sequel.